Field of the Invention
This invention relates to electrical feedthroughs of improved design and to their method of fabrication.
Electrical feedthroughs serve the purpose of providing an electrical circuit path extending from the interior of a hermetically sealed container to an external point outside the container. The conductive path is provided through the feedthrough by a conductor pin which is electrically insulated from the container itself. Many such feedthroughs are known in the art which provide the electrical path and seal the electrical container from its ambient environment. Such feedthroughs typically include a ferrule, the conductor pin or lead and a hermetic glass or ceramic seal which supports the pin within the ferrule. Such feedthroughs are typically used in electrical medical devices such as implantable pulse generators (IPG's). It has recently been discovered that such electrical devices can, under some circumstances, be susceptible to electromagnetic interference (EMI). At certain frequencies for example, EMI can inhibit pacing in an IPG. This problem has been addressed by incorporating a capacitor structure within the feedthrough ferrule thus shunting any EMI at the entrance to the IPG for high frequencies. This has been accomplished with the aforementioned capacitor device by combining it with the feedthrough and incorporating it directly into the feedthrough ferrule. Typically, the capacitor electrically contacts the pin lead and the ferrule.
One of the more popular materials for use as the pin lead is tantalum. Unfortunately, tantalum is susceptible to oxide growth which can, depending on its extent, act as an insulator instead of a conductor over the surface of the pin lead. During fabrication of a feedthrough/capacitor combination, the tantalum pin is subjected to one or more heat treatments which can encourage oxidation, affecting the conductivity of the tantalum pin lead and its ability to make good electrical connections between other elements including the capacitor and so forth.